package main

import (
	"fmt"
	"regexp"
)

func main() {
	str := "90120023036"
	re := regexp.MustCompile(`.{1,3}`)
	resultSlice := re.FindAllString(str, -1)
	result := ""
	for i, s := range resultSlice {
		result += s
		if i != len(resultSlice)-1 {
			result += ","
		}
	}
	fmt.Println(result)
}
